This invention relates to an electronic musical instrument, more particularly an electronic musical instrument having a plurality of musical tone production channels of the number lesser than the total number of keys.
In an electronic musical instrument having an upper keyboard generally used for a melody performance and a lower keyboard generally used for an accompaniment performance, the tone colors of the tones respectively produced by the upper and lower keyboards are usually different. To this end, it is necessary to provide a plurality of musical tone production channels for each of the upper and lower keyboards. This type of an electronic musical instrument is disclosed, for example in U.S. Pat. No. 4,192,211 dated Mar. 11, 1980. The number of the musical tone production channels for each of the upper and lower keyboards should be equal to the maximum number (for example about 10) of the tones which are produced simultaneously, because only the upper keyboard or the lower keyboard is performed with both hands. In a normal performance mode, however, in which both upper and lower keyboards are used, that is the melody performance is performed with the right hand using the upper keyboard and the accompaniment performance is performed with the left hand using the lower keyboard. In such a case, the number of the musical tone production channels actually used is substantially smaller (about 1 to 3 channels) than the total number of the tone production channels of the upper and lower keyboards, so that many tone production channels are left idle.
In an electronic musical instrument having a single keyboard, the keyboard is divided into high and low tone key ranges so as to perform a melody with the high tone key range and to perform an accompaniment with the low tone key range to produce tones of different tone colors. In the electronic musical instrument too, a plurality of independent musical tone production channels are provided for the melody and the accompaniment tones but the number of the channels of each group is not so large thereby decreasing the number of idle channels. However, where it is desired to perform a performance (for example to simultaneously produce a pluraity of tones with a melody tone color) apart from a predetermined performance mode (for example one tone for the melody and 3 concurrent tones for the accompaniment) such performance is impossible with an electronic musical instrument with a limited number of musical tone production channels for a melody.
For the reason described above, electronic musical instruments have been proposed as described in U.S. Pat. Nos. 4,351,214 and 4,365,532, said patents being owned by assignee of this application, in which, instead of fixing the relation between the musical tone production channels and the key ranges or keyboards, the relation is made variable according to the performance mode so as to utilize all musical tone production channels for producing melody tones over the entire key range or to utilize the musical tone production channels for the melody tone (a specific key range tone) or for the accompaniment tone (the other key range tone).
More particularly, in order to detect the specific note of the melody with the special musical tone production system it is necessary to take in an information representing a note (melody) assigned to musical tone production channels used to produce a melody and then detect a predetermined note (the highest note) out of the information. However, as above described, the range of the musical tone production channels utilized to produce a melody tone is changed in accordance with the performance mode, it is necessary to execute the detection operation by always taking into consideration the performance mode. If a predetermined note were detected from a definite channel range (for example all channels), a note (for example an accompaniment tone) different from the melody note would be detected thus causing the special musical tone production system to produce an unnatural tone.